Assaying method

ABSTRACT

The invention provides a method of assaying a mineral sample for determining the concentration of selected metals in a sample comprising the steps of providing a comminuted mineral sample; mixing such sample with a flux; preheating a reaction vessel to a temperature which approximates the melting point of the flux; introducing the mixture of the mineral sample and flux into the crucible, whereby the mixture is transformed to a molten state to capture the metal to be assayed in a collector material; and separating slag from the collector material.

FIELD OF THE INVENTION

[0001] THIS invention relates to assaying, and particularly, but notexclusively, to assaying gold and/or platinum group metals (PGM's), inan ore sample.

BACKGROUND TO THE INVENTION

[0002] It is common practice in gold or platinum mining and explorationoperations to assay the ore in order to quantify the amount of goldand/or PGM's (platinum, palladium, rhodium, osmium, iridium andruthenium) present.

[0003] The conventional assaying process is commonly known as “fireassay”. The process involves weighing an amount of a comminuted ore, andmixing it with a lead oxide bearing flux or nickel flux. The mixture isthen placed in a crucible and heated to elevated temperatures usuallyaround 1100 to 1250 degrees Celsius for a period of about 60 to 90minutes.

[0004] During this process the mixture melts, the lead oxide is reducedto lead metal or nickel sulfide is formed and the lead or nickel sulfideacts to collect the PGM's and/or gold due to their chemical affinity.

[0005] The molten slag and collector material is poured in to a mouldwhere it is allowed to cool. The lead or nickel sulfide settles to thebottom of the mould. Once the mould is cooled, the lead or nickelsulfide is separated from the slag using mechanical techniques. Theprocedure is labour intensive. Once the collector material has beenseparated from the slag, it is placed in a cupel which is pre-heated at1000 to 1300 degrees Celsius to allow the lead to be absorbed by thecupel. The result is a tiny prill left at the base of the cupel. ThePGM's and gold content in the prill can then be determined using anumber of analytical techniques.

[0006] Apart from the time consuming process described above, it hasbeen found that during the loading and removal of reaction vessels orcrucibles from a fire assay furnace considerable energy losses occurresulting in further delays in the assaying process.

[0007] Regarding the fluxes used in fire assay processes, conventionalcomponents of fluxes include borax (hydrated sodium borate), sodiumcarbonate, litharge (lead monoxide), silica, carbon, fluospar, red leadPb₃O₄) potassium nitrate, and iron.

OBJECT OF THE INVENTION

[0008] The object of the present invention is to provide a new method ofcollecting metals in a mineral sample in an assaying process.

[0009] A further object of the present invention is to provide a methodsand means for concentrating a metal collected in a collector and/orco-collector material.

[0010] A further object of the invention is the provision of methods andmeans for separating a metal collected in an assaying process, from amolten slag.

[0011] A further object of the invention is to provide a handlingmechanism and method which is suitable for use in an assaying process.

[0012] Yet a further object of the invention is to provide a novelreaction flux for assaying which it is believed will have advantagesover conventional fluxes.

[0013] A further object of the invention is to provide a handlingmechanism and method suitable for loading and removing crucibles,reaction vessels or the like into and removing the same from a furnace.

SUMMARY OF THE INVENTION

[0014] According to the present invention, a method for assaying amineral sample for determining the concentration of selected metals inthe sample, comprises the steps of:

[0015] providing a comminuted mineral sample;

[0016] mixing such sample with a flux;

[0017] preheating a reaction vessel to a temperature which approximatesthe melting point of the flux;

[0018] introducing the mixture of the mineral sample and flux into thecrucible, whereby the mixture is transformed to a molten state tocapture the metal to be assayed in a collector material;

[0019] and separating slag from the collector material.

[0020] Further according to this aspect of the invention, heat energy isadded to the reaction vessel and mixture once the latter has beenintroduced into the reaction vessel to cause fusion of the mixture.

[0021] In one embodiment of the invention, the collector material willbe lead or other material capable of being oxidized, and a furthermethod of the invention provides for the step of oxidizing suchcollector material to reduce the volume thereof, or a collectormaterial. In such a method, the re-oxidized collector material will thusbe recaptured by slag of the flux. This method may be applied toconventional assaying processes wherein the reaction vessel is notpreheated.

[0022] In the above aspect of the invention, the collector material isoxidized by introducing oxygen, or an oxygen producing material, intothe reaction vessel. Preferably, the oxygen will be introduced into thecollector material by means of a lance or the like.

[0023] In an alternative arrangement the reaction vessel can be providedwith a low level outlet and oxygen introduced into the reaction vesselthrough the low level outlet thereof for re-oxidizing collectormaterial. Thereafter, the collector material can be drained through thelow level outlet further analysis.

[0024] Also according to this aspect of the invention, the method mayinclude the step of introducing a separate collector for the material tobe assayed into the reaction vessel, such as silver or gold.

[0025] In an alternative arrangement the method of the invention mayinclude the step of separating the collector material from the slagformed during the fusion process, and thereafter contacting thecollector material with oxygen or oxygen forming material to oxidize thecollector material or a portion thereof. In this arrangement it ispreferable that a stream of oxygen gas will be blown onto, or into thecollector material for oxidization purposes. Thus in the cases wherecollector material includes lead, such lead will be oxidized to leadoxide which will be released as a vapor. Collector material such assilver which is not capable of being oxidized readily, will remain forassaying purposes.

[0026] In a further example oxygen may be introduced into the separationvessel from a supply source via a collection mould which sealinglyengages the separation vessel below the outlet duct therefrom.

[0027] Also according to this aspect of the invention, the methodincludes the step of disengaging the collection mould from theseparation vessel to permit the collected material to drain into suchcollection mould. Pressure in the collection mould thus serves to closethe outlet duct until the collection mould is disengaged from theseparation vessel.

[0028] Once the collected material has been discharged into thecollection mould, the material will be caused to fuse and to form aprill, and such prill can be deposited on a suitable transportationmeans for further processing.

[0029] Also included within the scope of the invention, is a apparatussuitable for use in the above method comprising a separation vessel,having a low level outlet duct, and a collection mould disposed belowthe outlet duct and adapted sealingly to engage the separation vessel,an inlet for oxygen or other gas in the collection mould to enableoxygen/gas to be ducted through the interior of the collection mould andthe low level outlet duct, into the separation vessel.

[0030] Also according to this aspect of the invention, the apparatusincludes lifter means whereby the collection mould can be lifted intoengagement with the separation vessel, and lowered to a position removedfrom the separation vessel.

[0031] Preferably, the separation vessel will include a downwardlydirected tube formation extending from the outlet duct, and againstwhich the collection mould sealingly engages.

[0032] The invention further provides a method of separating thecollector material from the slag, comprising the steps of providing acollector material which is of greater density and/or lower viscositythan the slag, providing a separating vessel which is provided with aoutlet duct, and draining the collector material through such outletduct, the arrangement being one wherein the dimensions of the outletduct are such that the collector material passes therethrough, while theslag is arrested at the duct. Preferably the outlet duct will bedisposed at the lower extremity of the vessel.

[0033] The invention is also directed separately to the separatingvessel described above and in one embodiment thereof, the vessel is of agenerally conical shape in cross-section, with the outlet duct beingdisposed at the lowermost pinnacle of the cone shape.

[0034] Where the collector material is lead, the outlet duct could forexample be of a circular cross-section having a diameter of between 0.5mm and 2.0 mm, preferably around 1.0 mm.

[0035] In an alternative arrangement, such a method of separatingcollector material from slag comprises the steps of providing aseparating vessel which defines an interior concavity which terminatesin a lower portion for receiving the collector material, and whichdefines an outlet duct in a position spaced from such lower portion, andcomprising the further steps of rotating the reaction and separatingvessel transversely so that collector material in the lower-mostportion, flows to the zone of the outlet duct; and draining suchcollector material through the outlet duct. As previously mentioned theproportions of the outlet duct will be such that the collector materialis capable of passing therethrough, while the slag is arrested.

[0036] With the above alternative method the vessel thus has a lowerportion for receiving collector material and an outlet duct spaced fromsuch lower portion, the outlet duct being such that the collectormaterial is capable of passing therethrough, while the slag is arrested,and a concavity in the zone of the outlet duct for receiving thecollector material when the reaction and separating vessel is rotatedangularly to cause the collector material to flow to the zone of theoutlet duct.

[0037] According to a different aspect of the invention a handlingmechanism for transporting an article such as a reaction vessel orcrucible into a furnace is provided comprising carrier means, thecarrier means being movable between a first position in which it isdisplaced from the furnace and a second position in which it mates withan aperture in the furnace; and drive means for moving the carrier meansbetween the first and second positions.

[0038] The handling mechanism described above is particularly suitablefor use in the fire assaying methods of the invention. Accordingly, thearticle may comprise at least a crucible containing a mineral sample anda flux therein.

[0039] Preferably, the aperture is located in a base portion of thefurnace and the carrier means is suitable for mating with the aperturewhen in the second position, effectively to close the aperture. Further,the handling mechanism according to the invention may include a loadingdevice for transporting an article to the carrier means when the carriermeans is in the second position. The loading device is preferably arobotic arm. The drive means is preferably a pneumatic reciprocatingram. Alternatively, the drive means may be a lever or a cam mechanism.

[0040] The invention further provides a furnace for use with thehandling mechanism described above, the furnace having at least oneaperture suitable for mating with the carrier means.

[0041] Separately included within the scope of the invention, is aprocess for heat treating an article for example in an assaying processcomprising the steps of:

[0042] providing a furnace as described above;

[0043] moving the carrier means to the first position;

[0044] loading the carrier with an aticle;

[0045] moving the carrier means to the second position such that thearticle is carried into the furnace; and

[0046] removing the article from the furnace after the requiredresidence time, by moving the carrier means to the first position.

[0047] According to yet a further aspect of the invention, a fluxsuitable for use in the fire assay methods of the invention includes acollector material adapted to combine with material in a mineral samplewhich is to be collected, and potassium hydroxide. For mostapplications, the flux will include between 5% and 60%, preferably 7.5%potassium hydroxide by weight.

[0048] Further according to this aspect of the invention, the fluxincludes one or more additional compounds selected from the alkalineearth metal group of compounds. Preferably, such alkaline earth metalgroup compounds will be hydroxides. Thus in one arrangement the flux mayinclude between 5% and 60%, preferably 7.5% by weight of calciumhydroxide.

[0049] Also according to the invention, the flux may include one or moreadditional compounds from the alkaline metal group, preferablyhydroxides. For example, the flux may include between 10% and 19% sodiumhydroxide, by weight.

[0050] In order more clearly to illustrate the invention, someembodiments thereof are described hereunder, purely by way of example,with reference to the accompanying drawings wherein:

BRIEF DESCRIPTION OF DRAWINGS

[0051]FIG. 1 is a flow diagram of a method of assaying in accordancewith the invention;

[0052] FIGS. 2 to 3 are schematic sectioned elevations of a reaction andseparating vessel which is employed in the method of the invention,illustrating various steps in such method;

[0053]FIG. 4 and FIG. 5 are schematic sectioned elevations of a reactionand separating vessel which is employed in a method of assaying inaccordance with the invention illustrating various steps in such method;

[0054]FIG. 6 and FIG. 7 are schematic sectioned elevations of a reactionand separating vessel which is employed in a method of assaying inaccordance with the invention illustrating various steps in such method;

[0055]FIG. 8 and FIG. 9 are schematic sectioned elevations of a reactionand separating vessel which is employed in a method of assaying inaccordance with the invention illustrating various steps in such method;and

[0056]FIG. 10 and FIG. 11 are schematic elevations of a handlingmechanism for introducing and removing reaction vessels into and from aheating furnace.

DESCRIPTION OF DRAWINGS AND EXAMPLES OF THE INVENTION

[0057] Referring to the drawings, a method of assaying in accordancewith the invention comprises the steps set out in FIG. 1. These stepscomprise providing a mineral sample shown at 10, normally in drypowdered form, and mixing (11) a predetermined weight of such samplewith a predetermined quantity of a suitable known flux which containslead oxide, nickel or on other material which is adapted to form acollector material for the analyte/metal mineral which is to be assayed.The method of the invention is in particular but not exclusively adaptedfor assaying gold or PGM's.

[0058] The mixture prepared as above, is next introduced into a reactionvessel (13). It is a feature of the invention that the reaction vesselwill be pre-heated (12) to a temperature in the region of the fusiontemperature of the mixture, in a suitable furnace or the like. Suchfurnace could for example be gas fired, electric or an inductionfurnace. Upon introduction of the mixture into the reaction vessel,further heat energy is supplied to the reaction vessel as shown at 14 tomaintain it at the fusion level of the mixture.

[0059] Upon fusion of the mixture, a collector material, such as lead ornickel sulfide, is formed at 15 and acts to collect the gold and PGM'sthrough chemical affinity. The collector material can thereafter beseparated from the slag as described below, for analysis.

[0060] One aspect of the invention, provides for the collector materialto be reduced in volume (16), and if necessary, to be concentrated by aco-collector material (17) in order to enhance the assaying process.Such reduction in volume is illustrated in FIG. 2 and comprises the stepof introducing oxygen 23 into the collector material 24, FIG. 2, forexample by means of a lance 21 which projects into the reaction vesselshown at 19, FIG. 2. The oxygen 23 thus reacts with the lead 24, orother collector material, which is capable of being oxidized, andoxidizes the lead to lead oxide which is recaptured in the slag 25. Withthis method, a small amount of lead 24 can be retained for assaying(18), or else, concentrated in a co-collector such as silver or goldwhich is more amenable to analysis, for example, by means of sparkspectrometry. The invention thus envisages that a separate co-collectormaterial could be added to the mixture prior to fusion or thereafter.

[0061] As an alternative to the use of the lance 21, the moltencollector material 24 can first be separated from the molten slag 19 anddeposited in a cupel in molten form, and at that stage contacted with arich source of oxygen, whereby the collector material 24 is oxidized orpartially oxidized. As previously mentioned, the collector material 24can comprise lead which is readily oxidized in such conditions, togetherwith silver as a co-collector which is not readily oxidized. During theoxidation process, the silver will thus remain to form a prill whichcontains the metal to be assayed. Such a prill will for example lenditself to analysis by gas release cromatographic analysis. Thus, thissource of oxygen can again for example be in the nature of a lance 21used for blowing oxygen gas onto or into the collector material 24, oralternatively, an oxygen producing salt can be introduced into thecollector material 24.

[0062] Alternatively with reference to FIGS. 9 and 10 oxygen can beintroduced through the low level outlet 20 of the reaction vessel 19 viaa collector vessel 131 and a tubular extension 121 of the reactionvessel 19.

[0063] The invention further provides for a methods of separating themolten collector/co-collector material 24 together with the gold orPGM's contained therein, from the molten slag 19.

EXAMPLE 1 OF A SEPARATING VESSEL

[0064] One method comprises the provision of a separating vessel 19illustrated in FIGS. 2 and 3.

[0065] The vessel 19 is of a generally conical profile with thetermination 19 a of the cone facing downwardly. An outlet duct 20 isprovided co-axially with the lower termination 19 a of the cone 19, andis adapted in use to drain the collector material 24 from the vessel 19into a suitable vessel or mould 26, FIG. 3. The invention envisages thatthe collector material 24 will be of a greater density and/or a lowerviscosity than the molten slag 25 and the proportions of the outlet duct20 will be such that only the collector material 24 is capable offlowing through the duct 20. Thus in the case of lead, the lead willreadily drain through the outlet duct 20, while the molten slag 25 willbe arrested at the outlet duct 20 and incapable of passing therethroughas a result of the lower density and viscosity thereof, as shown in FIG.3. It has been found that an outlet duct 20 of generally circularcross-section with a diameter of between 0.5 mm and 2.0 mm preferablyaround 1.0 mm, will be suitable.

[0066] It will be appreciated that the size of the aperture could berendered adjustable to suit requirements, for example by providing asuitable valve, not shown, or stopper for such outlet duct 20. One sucharrangement is shown in FIG. 2 wherein the oxygen lance 23 terminates ina plug formation 22 which is axially movable between a position whereinit engages the lower end 19 a of the vessel 19 to seal the outlet duct20, and a position wherein the plug 22 is displaced from the lower end19 a of the vessel 19 to open the outlet duct 20. With such anarrangement therefor, the separating vessel 19 can also be utilized as areaction vessel by closing the outlet duct 20 until separation of thecollector material 24 and the slag 25 is required. Thus during fusion ofthe mixture 15, FIG. 1, and the step of oxidizing the collector material16, FIG. 1, the plug 22 will be in its closed position. Subsequently, itwill be opened to effect separation between the collector material 24and the slag 25 as described above.

EXAMPLE 2 OF A SEPARATING A VESSEL

[0067] In this example with reference to FIGS. 4 to 7, a reaction andseparating vessel 19 comprises a body member which defines an interiorconcavity 32 which includes a lowermost portion 32 a for receiving acollector material 24 during an assaying procedure. Thus, during theprocess of causing fusion of a mixture of a flux material and a mineralsample, a collector material 24 in the form of lead or nickel sulfide orsilver or the like is formed and serves to capture gold and PMG'spresent in the mineral sample. The collector material 24 being ofgreater density settles in the lowermost zone 32 a of the reaction andseparating vessel, while a slag 25 which includes gangue, overlies thecollector material 24. As disclosed above, oxygen may be introduced intothe collector material 24 to oxidize all, or a portion thereof, which isthen reabsorbed in the slag 25.

[0068] The reaction and separating vessel 29 of the present disclosureis characterized in the provision of an outlet duct 20 which is locatedoutside the lowermost zone 32 a of the concavity 32, which receives thecollector material 24. In the arrangements illustrated, the outlet duct20 is located in the side wall of the vessel 29, but the invention isnot limited to such a location and clearly other positions could also befunctional.

[0069] It is a feature of the invention that the collector material 24,or the remainder thereof after oxidization, is separated from the slag25 by rotating the reaction and separating vessel 29 transversely, sothat the collector material 24 flows to the zone of the outlet duct 20,and is received in the outlet duct concavity 30. From the outlet ductconcavity 30, the greater density and/or lower viscosity of thecollector material 24 permits such material to be drained through theoutlet duct 20, whereas the slag 25 is arrested and cannot flow throughthe duct 20. As disclosed above, the proportions of a circular outletduct 20 could be between 0.5 mm to 2.0 mm, preferably 1.0 mm indiameter.

[0070] Preferably, the outlet duct 20 will include a concavity 30 intowhich the collector material 24 will flow prior to, or upon, beingdrained through the duct 20. If required, a groove or pathway, notshown, could also be provided on the inner surface of the vessel 29 todirect the collector material 24 from the lowermost portion 32 a of thevessel 29 to the outlet concavity 30.

[0071] In the arrangement illustrated in FIGS. 4 and 5; the vessel 29 isrotated through approximately 90 degrees in order to position the outletduct 20 at a lower-most position of the rotated vessel 29 for purposesof draining the collector material 24 therefrom. In the arrangementillustrated, the outlet duct 20 is disposed in a side wall of the vessel29, but clearly this position can vary in accordance with therequirements, and could for example be disposed in a roof portion of thevessel. It will be understood that the position of the outlet duct 20will determine the angle through which the vessel 29 should be rotatedin order to cause the collector material 24 to flow to such outlet duct20 for drainage purposes.

[0072] In the arrangement shown in FIGS. 4 and 5, the outlet ductconcavity 30 is formed by an outward bulge 29 a of the side wall of thevessel 29.

[0073] In an alternative arrangement shown in FIGS. 6 and 7, the outletduct concavity 30 is formed by an inwardly directed shoulder 29 b of theinner wall of the vessel 29. With this arrangement, the vessel will berotated through an angle which is greater than 90 degrees in order toposition the vessel 29 so that the outlet duct concavity 30 is disposedlower-most. In such a position, the slag 25, or at least a portionthereof, will overflow from the vessel 29 as shown in FIG. 7, and can becollected separately. Thus the arrangement will be such that all theslag 25 is decanted in such position, while the collector material 24 isdrained through the duct 20.

[0074] In both examples described above, FIGS. 4 and 5 and FIGS. 6 and7, the outlet duct 20 may be provided with valve or stopper means forselectively draining collector material 24 from the vessel.

EXAMPLE 3 OF A SEPARATING VESSEL

[0075] Referring to FIGS. 8 and 9 separating means for use in the assaymethod in accordance with the invention comprises a separation vessel 19which is generally conically shaped and which terminates in a low leveloutlet duct 20. Below the outlet duct 20, a short length of ceramic tube121 depends downwardly from their separation vessel 19.

[0076] The apparatus further includes a collection mould 131 which isdisposed co-axially below the ceramic tube 121, and which is movably bymeans of a lifter 141 such as a hydraulic ram from a position removedfrom the ceramic tube as shown in FIG. 8; to a position wherein itsealingly engages the ceramic tube, FIG. 9. The collection mould 131further includes a inlet 15 for oxygen 161 in the side wall thereof.With this arrangement, it is therefore possible to introduce oxygen 161from a supply source, not shown into the separation vessel 10 via theinterior of the collection mould 14 and through the outlet duct 11 fromthe separation vessel 10.

[0077] In an assaying method using the above apparatus, a mixture of acomminuted mineral sample, and a assaying flux will be introduced into aseparation vessel. The flux will for example include lead oxide whichwill form slag and lead in a reaction process, the latter combining withthe gold and/or PMG's as a result of chemical affinity. At this stage,heat is supplied to the separation vessel and/or material therein. Theseparation vessel may also be preheated as disclosed above. At thisstage, the collection mould 131 will be engaged with the ceramic tube121 oxygen 161ducted and introduced into the separation vessel 19 viathe interior of the collection mould 13 land outlet duct 20 while themolten slag and lead is added to the separation vessel 19. Oncesufficient time has elapsed, the oxygen supply is shut-off. At thisstage the collector material such as lead has been re-oxidized to redoxide for absorption in the molten slag.

[0078] Pressure in the collection mould 131 will however at this stagelimit discharge of material through the outlet duct 20 of the separationvessel 19. The next step of the process comprises lowering thecollection mould 13 from the separation vessel 19 by means of thehydraulic ram 141, causing collected material 24 to drain through theoutlet duct 20 into the collection mould 131. The diameter of the outletduct 20 is such that the relatively dense and low viscosity collectedmaterial 24 will pass through the duct 20, while the slag 28 will bearrested within the vessel 19. The collection mould 131 which isrelatively insulated from the heat of the separation vessel 19 by meansof the ceramic tube 121 will be relatively cool and the collectedmaterial 24 will rapidly solidify in the collection mould 131, to form aprill of material. Thereafter the collection mould 131 can be tilted todischarge the prill 24 onto suitable conveying means, not shown, forfurther processing. At this stage also the separation vessel 19 can betilted to discharge remaining slat 25 in the vessel 19 which isimmediately available for re-use.

[0079] A further aspect of the invention comprises a handling mechanismwhereby reaction vessels, crucibles, etc., which are used in a fireassay method can be loaded into and out of a furnace efficiently withoutundue loss of energy.

[0080] Such handling meachanism 10 consists of carrier means in the formof a number of level platforms 16 of refractory material, each of whichare driven by a reciprocating ram 17, typically a pneumatic cylinder.Each platform 16 is movable between a first position in which it isdisplaced from the furnace 14 (shown in FIG. 2) and a second position inwhich it mates with a corresponding aperture 18 in the furnace 12 (shownin FIG. 1).

[0081] The apertures 18 are located in a base portion of the furnance 14and each platform 16 is suitably dimensioned for mating with acomplementary aperture 18 when the platform 16 is in the secondposition, effectively to close the aperture 18.

[0082] A loading device in the form of a robotic arm 20 is provided forloading/unloading the crucible 12 onto/from the platform 16 when theplatform 16 is in the first position.

[0083] In use, a crucible 12 containing at least a mineral sample andflux is prepared for heat treatment in the furnace 14. One of theplatforms 16 is moved into the first position, in which it is displacedfrom its complementary aperture 18 in the base portion of the furnace14. The robotic arm 20 loads a crucible 12 onto the platform 16. Thereciprocating ram 17 moves the platform 16 into the second position, andthe crucible 12 is received into the furnace 14 through the aperture 18.The platform 16 mates with the aperture 18 so as effectively to closethe aperture 18.

[0084] After the required residence time, the reciprocating ram 17retracts, displacing the platform 16 away from the furnace 14, into thefirst position. When in the first position, the crucible 12 containingmolten flux is removed from the platform 16 with the robotic arm 20.Once the crucible has been removed, the platform is moved back into thesecond position, to prevent heat escaping from the furnace 14 throughthe aperture 18.

[0085] It is envisaged that the handling mechanism will be useful in afire assaying method in that sample carrying crucibles can be heatedconsecutively and on a continuous basis as opposed to a batch basis, toprevent heat escaping from the furnace when the crucibles are removed.Because the crucibles are not heated on a batch basis, the apparatus andmethod according to the invention has a further advantage in that thecrucibles do not cool substantially, which reduces the time required topreheat the crucibles prior to assaying.

[0086] Yet a further aspect of the invention comprises the provision ofa novel flux which has been found to provide a particularly rapidreaction time is provided.??

[0087] In one example of a flux in accordance with the invention,suitable for assaying of gold ores and Platinum Group element ores couldtypically have the following composition: Potassium hydroxide 7.5%Calcium hydroxide 7.5% Sodium hydroxide  10% Borax  31% Litharge  30%Sodium carbonate 7.0% Silica 6.5% Carbon 0.5%

[0088] In practice, the above composition will be used in quantities ofapproximately 200 grams for purposes of assaying gold ores and PlatinumGroup metal ores. For mine tailings quantities up to 500 grams might beused.

[0089] It has been found that the composition above, dramaticallyincreases the rate of fusion of the flux during fire assay.

[0090] It has also been found that the action of the potassium hydroxideis further enhanced by the addition of sodium hydroxide. It has beenfound that a synergistic effect is created by the use of these twoalkaline metal hydroxides.

[0091] The exact composition of the flux will vary in accordance withthe types of ores to be assayed. Thus for example, the quantity ofpotassium hydroxide could vary between 5% and 60%, calcium hydroxidebetween 5% and 60%, and sodium hydroxide between 10% and 19%. Inaddition the flux composition could include fluorspar, red lead,potassium nitrate, and iron.

[0092] The advantages of the various aspects of the invention will beunderstood by persons skilled in the art. The processes of the inventionreadily lend themselves to mechanization and computerization. It willalso be understood that the accuracy of the assaying process will beenhanced, and the time period required therefor, greatly reduced.

[0093] Doubtless variations of the invention in detail exist withoutdeparting from the principles set out in the consistory clauses. Theinvention is directed separately to a method of assaying as describedabove, as well as to a method of reducing the volume of a collectormaterial, and/or concentrating in a co-collector material for the metalto be assayed, and also to a method and means for separating acollector/co-collector material from a molten slag.

1. A method of assaying a mineral sample for determining theconcentration of selected metals in a sample comprising the steps of;providing a comminuted mineral sample; mixing such sample with a fluxwhich forms a collector material during fusion thereof; causing themixture to fuse whereby the mixture is transformed to a molten state toform a slag and to capture the metal to be assayed in a the collectormaterial; and separating the slag from the collector material;characterized in that the collector material is separated from the slagby allowing the collector material to drain through au outlet apertureby force of gravity, the dimensions of the aperture being sufficientlyrestricted to prevent the slag from draining through the aperture byforce of gravity.
 2. The method according to claim 1 wherein thereaction vessel is preheated prior to introducing the mixture into thereaction vessel to cause fusion of the mixture.
 3. The method accordingto claim 1 or claim 2 wherein the method includes the step of oxidizingthe collector material or portion thereof before or after fusion of themixture to reduce the volume of the collector material.
 4. The methodaccording to claim 3 wherein the collector material is oxidized byintroducing oxygen or an oxygen producing material into the reactionvessel after fusion of the mixture.
 5. The method according to claim 3or claim 4 wherein oxygen is introduced into the collector material bymeans of a lance or the like.
 6. The method according to claim 3 orclaim 4 wherein oxygen is introduced into the collector material througha low level outlet aperture of the reaction vessel for oxidizing thecollector material, prior to drawing of the collector material throughsuch outlet aperture.
 7. The method according to claim 6 wherein oxygenis introduced into a separation vessel through the low level outletaperture from a supply source via a collector mould which sealinglyengages the separation vessel below the outlet aperture.
 8. The methodaccording to claim 7 including the step of disengaging the collectionmould from the separation vessel after oxidization of the collectormaterial to release pressure in the collection mould to permit thecollector material to drain into such collection mould, through theoutlet aperture.
 9. The method according to any one of claims 3 to 8including the step of introducing an additional collector material whichis resistant to oxidization into the reaction vessel, after or prior tofusion of the mixture and prior to oxidation of the collector material.10. The method according to claim 9 wherein the additional collectormaterial is silver or gold.
 11. The method according to any one ofclaims 1, 9, and 10, including the step of separating the collectormaterial from the slag after fusion of the mixture, and thereaftercontacting the collector material with oxygen or oxygen forming materialto oxidize the collector material or a portion thereof, to reduce thevolume of the collector material.
 12. The method according to claim 11wherein a stream of oxygen gas is blown onto or into the collectormaterial for oxidization purposes.
 13. The method according to any oneof claims 1 to 12 wherein the outlet aperture for collector material isdisposed at the lower extremity of the vessel.
 14. A method according toany one of claims 1 to 12 including the steps of separating thecollector material from the slag comprising providing a separatingvessel which defines an interior concavity which terminates in a lowerportion for receiving the collector material, and which defines anoutlet cavity in a position spaced from such lower portion, the outletcavity including an outlet aperture for draining collector material fromthe outlet cavity by force of gravity, the dimensions of the outletaperture being sufficiently restricted to prevent the slag from drainingthrough the outlet aperture by force of gravity, and comprising thefurther steps of rotating the reaction and separating vesseltransversely so that collector material in the lower-most portion flowsto the outlet cavity; and draining such collector material from theoutlet cavity through the outlet aperture.
 15. A method of assaying amineral sample according to claim 1 substantially as herein describedand exemplified with reference to the accompanying drawings andexamples.
 16. A method of assaying a mineral sample for thedetermination of the concentration of selected metals in the samplecomprising the steps of preparing a mineral sample; mixing the mineralsample with a flux which forms a collector material during fusionthereof; introducing the mixture into a reaction vessel, causing themixture to fuse whereby the mixture is transformed to a liquid state toform a flux and to capture the metal to be assayed in the collectormaterial; separating the collector material from the slag; characterizedby contacting the collector material with oxygen or an oxygen formingmaterial to oxidize the collector material or a portion thereof toreduce the volume of the collector material, before or after separationof the collector material from the slag.
 17. The method according toclaim 16 wherein the collector material is oxidized by introducingoxygen or an oxygen producing material into the reaction vessel afterfusion of the mixture before separation of the collector material fromthe slag.
 18. The method according to claim 17 wherein oxygen isintroduced into the collector material by means of a lance or the like.19. The method according to claim 17 wherein oxygen is introduced intothe collector material through a low level aperture for drainingcollector material from the reaction vessel.
 20. The method according toclaim 16 wherein oxygen is introduced into the separation vessel throughthe low level aperture for draining collector material from theseparation vessel from a supply source via a collector would whichsealing engages the separation vessel below the outlet aperture.
 21. Themethod according to claim 20 including the step of disengaging thecollector mould from the separation vessel after oxidation of thecollector material to permit collector material to drain into suchcollection mould, through the outlet aperture.
 22. The method accordingto any one of claims 16 to 21 including the step of introducing anadditional collector material which is resistant to oxidization into thereaction vessel after or prior to fusion of the mixture and prior tooxidation of the collector material.
 23. The method according to claim22 wherein the additional collector material is silver or gold.
 24. Themethod according to claim 16 including the step of separating thecollector material from the slag formed during the fusion process, andthereafter contacting the collector material with oxygen or oxygenforming material to oxidize the collector material or a portion thereofto reduce the volume of the collector material.
 25. The method accordingto claim 16 wherein a stream of oxygen gas is blown onto or into thecollector material for oxidization purposes.
 26. A method of assaying amineral sample according to claim 16 substantially as herein describedand exemplified with reference to the accompanying drawings andexamples.
 27. Apparatus suitable for use in the method claimed in anyone of claims 1 to 26 comprising a separation vessel, an outlet aperturefor draining collector material from the vessel by force of gravity, thearrangement being one wherein the dimensions of the outlet aperture aresufficiently restricted to prevent the slag from draining through theoutlet aperture by force of gravity.
 28. Apparatus according to claim 27wherein the aperture is substantially circular in cross-section and hasa diameter of between 0.5 mm to 2.0 mm.
 29. Apparatus according to claim28 wherein the aperture has a diameter of 1.0 mm.
 30. Apparatusaccording to claim 27 substantially as herein described and exemplifiedwith reference to the examples and accompanying drawings.
 31. Apparatussuitable for use in the method claimed in claim 5 or claim 16 comprisinga reaction or separating vessel and a lance device projecting into thevessel for introducing oxygen into the vessel.
 32. Apparatus accordingto claim 31 wherein the leading end of the lance acts as a stopper forany outlet aperture of the vessel, and the lance is longitudinallymoveable towards and away from the aperture to close and open suchaperture.
 33. Apparatus according to claim 31 substantially as hereindescribed and exemplified with reference to the accompanying drawingsand examples.
 34. Apparatus suitable for use in the method claimed inclaim 1 or claim 16 comprising a reaction vessel having a low leveloutlet aperture for draining collector material from the vessel by forceof gravity, the dimensions of the aperture being sufficiently restrictedto prevent slag from draining through the aperture by force of gravity,and a collection mould disposed below the outlet aperture and adaptedsealingly to engage the separation vessel, and an inlet for oxygen orother gas in the collection mould to enable oxygen or gas to be ductedthrough the interior of the collection mould and the low level outletaperture into the separation vessel.
 35. Apparatus according to claim 34which includes a lifter means whereby the collection mould can be liftedinto engagement with the separation vessel and lowered to a positionremoved from the separation vessel.
 36. Apparatus according to claim 34or claim 35 where the separation vessel includes a downwardly directedtube formation extending from the outlet aperture and against which thecollection mould sealingly engages.
 37. Apparatus according to claim 34substantially as herein described and exemplified with reference to theaccompanying drawings.
 38. Apparatus suitable for use in the methodclaimed in claim 1 or claim 16 comprising a separating vessel whichdefines an interior concavity which terminates in a lower portion forreceiving a collector material and which defines an outlet cavity forreceiving collector material in the position spaced from such lowerportion, the outlet cavity including an outlet aperture for drainingcollector material from the outlet cavity by force of gravity, thedimensions of the outlet aperture being sufficiently restricted toprevent slag from draining through the outlet aperture by force ofgravity.
 39. Apparatus according to claim 38 therein the separatingvessel is rotateable angularly to cause the collector material to flowto the outlet cavity.
 40. Apparatus according to claim 38 substantiallyas herein described and exemplified with reference to the accompanyingdrawings.
 41. A handling mechanism suitable for use in the methodclaimed in claim 1 or claim 16 for transporting an article such as areaction vessel into an out of a furnace comprising carrier means, thecarrier means being movable between a first position in which it isdisplaced from the furnace and a second position in which it mates withan aperture in the furnace; and drive means for moving the carrier meansbetween the first and second positions.
 42. A handling mechanismaccording to claim 41 wherein the aperture is located in a base portionof the furnace and the carrier means is shaped and configured to matewith the aperture when in the second position, effectively to close theaperture.
 43. The handling mechanism according to claim 41 or claim 42wherein the handling mechanism includes a loading device fortransporting an article to the carrier means when the carrier means isin the second position.
 44. The handling mechanism according to claim 43wherein the loading device is preferably a robotic arm.
 45. The handlingmechanism according to any one of claims 41 to 44 wherein the dive meansis a reciprocating ram lever, or cam mechanism.
 46. A handling mechanismaccording to claim 41 substantially as herein described and exemplifiedwith reference to the drawing and examples.
 47. A furnace suitable foruse with the handling mechanism claimed in any one of claims 41 to 46having at least one aperture adapted to mate with the carrier meanssubstantially to seal such aperture when the carrier means is in itssecond position.
 48. A furnace according to claim 47 substantially asdescribed and exemplified with reference to the accompanying drawingsand examples.
 49. A process for treating an article in a furnacecomprising the steps of providing a furnace as claimed in claim 47 orclaim 48 and a handling mechanism as claimed in any one of claims 41 to46; moving the carrier means to the first position; loading the carrierwith an article; moving the carrier means to the second position suchthat the article is carried into the furnace; and removing the articlefrom the furnace after the required residence time, by moving thecarrier means to the first position.
 50. A process for treating anarticle in a furnace according to claim 49 substantially as hereindescribed and exemplified with reference to the examples and drawings.51. A flux suitable for use in the method claimed in claim 1 or claim 16which includes the collector material adapted to combine with materialin a mineral sample further including potassium hydroxide material. 52.The flux according to claim 51 including between 5% and 60%, preferably7.5% potassium hydroxide by weight.
 53. The flux according to claim 51or claim 52 including one or more additional compounds selected from thealkaline earth metal group of compounds.
 54. The flux according to claim53 wherein such alkaline earth metal group compounds are hydroxides. 55.The flux according to claim 54 including between 5% and 60%, preferably7.5% by weight of calcium hydroxide.
 56. The flux according to any oneof claims 51 to 55 including one or more additional compounds selectedfrom the alkaline metal group, preferably hydroxides.
 57. The fluxaccording to claim 56 including between 10% and 19% sodium hydroxide, byweight.
 58. A flux according to claim 51 substantially as hereindescribed and exemplified with reference to the examples.